A heavier propane cylinder would certainly be practical for a kayak or canoe trip, where such luxuries are commonplace.
The other nice thing about propane is that if you buy a 2 pack at Wal-Mart, it's
$2.56 for 465g. If you buy a 450g standard threaded backpacking gas canister, it's
$9.00, over three times more.
The big propane canister is heavy, but if say you were doing trailhead camping the night before a trip or you were doing "basecamp" style* hiking, then it wouldn't be too bad.
As you say, for canoeing and rafting it wouldn't be too bad. Even things like snowmobiling, a more compact stove might be nice. A lot of the single burner propane stoves I've seen are pretty big affairs.
HJ
*Backpack into a location, set up a base camp, and then just do day trips in and around the base camp. In other words, not carrying a full pack the whole time.