I've taken to buying bags of dried garbanzo beans instead of canned, however, no matter how long I soak them, they never expand to be as large as the canned, pre-cooked variety. This means when I try to roast them according to most of the recipes I find, they end up burned. I know there are different types of beans in that family, but the canned kind and the dried kind do appear to be the same. Can anyone tell me where the discrepancy in size comes from? 
Dried beans swell when soaked, and swell further when cooked. Your question implies that you are only soaking, not cooking the dried beans - which would both mean they would not get as large as the cooked canned ones, and that they would presumably roast differently than the cooked canned ones. I employ the difference in making felafel with soaked, dried beans rather than canned beans - the soaked, dried beans need no binder, while cooked or canned beans need some sort of binder such as wheat flour. It may well be possible to roast soaked, dried, uncooked beans, but it may require different time and temperature than cooked/canned ones. Incidentally, if you have the time, cooking your own from dried (when you want cooked beans) is far superior to canned ones on all fronts (taste, cost, amount of salt, etc.) except being exceedingly fast. 