If you could go during our "winter" (lol), say Jan through March, then the wetlands in Florida would be exactly what you are looking for, and would have tolerable temperatures. And the birds are nesting en masse right now, too!
Right now here in East Orlando it is 80 deg F, or 27 deg C, and we've had cooler days throughout January and so far into Feb. In May, the Orlando area gets up to 90 deg F, or 32 deg C, on average - but it will often be cooler at the coast (e.g. Cape Canaveral Wildlife area, or the beaches for shore birds - average temps there in May are 82 deg F, or 28 deg C). And some days will be cooler, and some warmer, of course.
The wetlands around Vancouver / coastal BC sound like a good suggestion for you, though!