ok I have been doing tons of reading of the forum and articles and backpacker and have a good idea of what gear I need and have started making a list..I am brand new to hiking let alone backpacking but am hoping to start building up to doing 100 miles of the john muir trail next august.I was looking at backpacks at REI and found a couple I actually liked(just informally no sales rep help)One, was large enough to accommodate the canister one was not..this started me thinking, can one strap the canister to the outside of their pack? or do you need a pack large enough to place inside? any pros or cons either way?

I've seen it done both ways, but I would urge you to find a way to carry it on the inside. A full bear canister is heavy and the smooth plastic is slippery. Unless really really well secured, the can can become something with a sort of mind of its own, shifting around and making you wonder if it's not going to slide out and fall down into a ravine.

What I've found works is to just strap more stuff on the outside to give more room for the canister. My pack has external mesh, which helps a lot in this, but in general, lots of other gear will work better if strapped externally than a bear can.

I'm NOT saying that an external carry for a canister won't work. If you do go that way, however, I recommend that you do one or more day hike somewhere with your pack just as you anticipate it and see how it works for you, not just walking a few paces with it in your house.

I have thought about this some, but there are problems to carrying it externally (many mentioned in post above mine). An internal frame pack does not have many good spots to carry a bear can. They are heavy and carrying them on top makes for an unstable top heavy pack. Most internal packs don't have much room underneath to strap on a bear can. You definitely don't want it banging into your butt or legs. The classic old external packs have a nice spot but they tend to heavier packs and very stiff (the load doesn't move with you). Strapping it on the side of the pack would be worse for your balance than strapping it on top.

These things are heavy and it is best to get them as close to your backbone as possible. One thing you can do is get the right sized bear can for your trip. I bought a lighter1 Lil' Sammi for weekend trips. I think it is smaller diameter than other IGBC approved canisters. It fits nicely in pack but doesn't work very well for groups or week long trips.

thank you both, It seems inside the pack is the best choice.

You want to be able to carry the canister sideways, not vertically. I've done the latter arrangement and it was not only extremely uncomfortable but made it really hard to pack! Of course that means a larger pack!
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Be sure to have all or most of your other gear (especially your bear canister!) before shopping for your pack--it should really be the last item you purchase. The pack must not only fit you; it must fit your gear and be comfortable for you with your gear inside. If possible, box up everything and take it to the store with you.

Have you read the articles on the home page of this site, left hand column? Lots of info there about packs and other gear.

Funny, but I think it depends on the person and the pack. I've carried my Bearvault for nearly ten years vertically inside my pack. Tent goes down right next to it along with some clothes, and everything stays tight and is easy to work with. Our can would not fit in our pack horizontally.

I see backcountrygear sells one of those zipped, web-handled "jackets" for canisters (since they sponsor, I hope it's ok to mention here, and I promise I have no connection): http://www.backcountrygear.com/backpackers-cache-bear-container-carrying-case-green.html

I've used either that exact jacket or a very similar one with Girl Scouts to strap a canister to the outside of a pack. Worked fine, but so did carrying the can inside. I find it easier to balance pad and/or bag on the outside, with canister on the inside. If shaving weight, you could compare waterproof sack for your bag versus the can case.

Oh, and the jacket can also make it super-easy to tether the can to something so it doesn't roll away. I have heard of frustrated bears using the cans as soccer balls, but never experienced it. 'course, tetherball might be fun, too.

I have one of those "jackets". It's sized to fit the Garcia canister; it's a very tight fit, won't fit a full-sized Bear Vault or Bearicade.

It's not waterproof; I'm not sure what you mean in comparing it to a waterproof sack. If you're thinking of an odorproof liner, then if anything I'd think this unit would have the opposite effect: not prevent odors from coming out, and offer a surface to spill/stain food on the outside.

I DON'T mean to say that I'm against this unit, other than the weight. Given how tight the fit on mine is and how much stress there is on the seams when the canister is full, I might be a little nervous to totally depend on it, but it absolutely does offer both friction and straps to connect the canister securely.

However, I don't tend to use it. In part because I prefer my Bear Vault canister over the Garcia, but the straps offer just a limited set of ways to connect things, and Murphy's law suggests that they just won't line up well with whatever point(s) are best for you to attach the can to. Also, you still have the weight of this thing to perhaps overbalance you, and if your pack isn't itself rigid and not absolutely full, then you could also have some sag factor such that the can doesn't stay still enough as you walk. Again, I'm not saying this has no place, just that I personally found its use more limited than I would have guessed.

Before buying this, I would suggest that someone that owns a Garcia can (the sort of traditional black plastic one that you need a coin or the like to open) --- take some frictional cord and wrap it several times at two points to simulate the points at which this thing offers strapping. I find the stuff that my mom used back in the day for clothes line to work well. Wrap several times and tie tight, leaving (tight, limited) loops at each warp, or just wrap right around what you want to tie down to as a test. Fill up your pack and take a decently long hike with it to see how it will hold up after a few hours of walking.

One problem is that such a cover (or attached straps) gives the bear a very convenient way to carry the canister away. At least for in-camp use, that's probably not a very good idea.