I own a Garcia and a BV450. I have never toured with either. I most often use the BV450 when backpacking and usually limit myself to trips where I can resupply with it's capacity range. I am getting to where I don't want to carry more than that these days any way. The Garcia is only for canoe camping for me these days. Where I have toured there have generally been bear boxes or I have been able to get by with hanging my food or other measures if critters were a problem. Once in a great while I was in a place where there was a threat of problems and no trees. In those VERY few cases I put my food away from camp and hoped for the best. I got by with it, but I have considered an Ursack for those places where I needed something and a hang was impossible or inadequate. That was a rare occurrence because anywhere that I have been that required canisters in the backcountry had bear boxes in the campgrounds, so I didn't need a canister on road tours and only rarely couldn't use a hang or some other means.

More to your question... Garcia sells a cover for their canister that makes it easy to strap it down. As was mentioned, take it out of the cover at night or the bears will be able to carry it. The BV 450 fits easily in all of my backpacks down to the 45 liter one so I think it would fit in many panniers.

How much food do you need to carry? Many of us try to minimize how much food we carry and restock very frequently. If that is the case for you using a very small canister may help as it fits in other baggage. You lose the advantage of it being as comfortable of a seat though. There are only a few small ones available though and they are not carried widely by retailers. The BV450 is the one I have. The little Scout Bearikade is a pricey $275, but is superlight. The Bare Boxer in another tiny one, but I have never even seen one of these.

Edit: I should have mentioned that the BV 450 isn't all that limited in how much food it carries in a road touring context. If you are going to into the backcountry and away from resupply for longer distances it is a different story.. With careful packing I can go 4 days or so when backpacking, but it requires careful packing and food choices. You are likely to fit less than that when touring unless you treat food choices as if you are backpacking by choosing stuff that packs well. I don't go the freeze dried route even when backpacking, but the amount of fresh food carried in a small canister would be limited. You could carry compact stuff and supplement with fresh food those days when it was available.