Can a Canadian man marry a man who is a US citizen?

Yes, there is no citizenship or residency requirement for marriage in either the US or Canada. However, if they marry in the United States, they will have to marry in a state that permits same-sex couples to marry (see related question below). They may, however, marry in any province in Canada.
Because of current federal law, the American citizen may not sponsor his Canadian husband for US citizenship. However, the Canadian citizen can sponsor his American husband for Canadian citizenship.
Yes, there is no citizenship or residency requirement for marriage in either the US or Canada. However, if they marry in the United States, they will have to marry in a state that permits same-sex couples to marry (see related question below). They may, however, marry in any province in Canada.
Because of current federal law, the American citizen may not sponsor his Canadian husband for US citizenship. However, the Canadian citizen can sponsor his American husband for Canadian citizenship.