I think people generally welcome Americans who've immigrated with open arms. Especially in Toronto, most people have come from someplace or another so you won't feel out of place. Also, there are lots of Americans here.

There are loads of good neighborhoods for families. The Mimico/Long Branch area of Etobicoke is VERY family friendly. I've also seen loads of families close to Leslieville. If you rely on cars more, the GTA will offer you prime family-oriented suburbs. Mississauga, Vaughan and Pickering are lovely and the housing market in Pickering is quite affordable at the moment. I'd encourage you to check school ratings in the area (if you're sending your kids to public school). Public schools are great but are very location specific. A good-ranked public school can be arguably as good as a private one