Nuvi 350 is quite sleek and the text to speech feature is very nice plus the custom POI list you can load up.
c550 has bluetooth, allows you to set it up for handsfree calling with your phone. The rest is pretty much similar.
You can increase storage by SD Card, which is v.v. cheap these days, load up music, play through the GPS, connect to car stereo, it lowers the volume when instructions are needed. Very useful on the longer trips.
If handsfree calling is not important, I'd opt for the Nuvi. Check around the online Canadian GPS stores, you can get a factory refurbished unit quite cheap with full warranty sometimes.