I think that Candian government should dollarize. I think it can only help them, because American dollar is higher then canada. Most of the American countries are dominated by US dollar and if Canada dollarizes they would have part of that world as well, because there isn't too much difference between American and Canadian dollar.
Canada is doing fine having its own currency, and has been since its inception. There is no clear reason why Canada should adopt the US dollar and, subsequently, have both countries exposed to the risks and economic issues of the other country. In Canada, many stores in major cities will accept the US dollar, and many US cities near the border will also openly accept Canadian currency as well (including tolls).