Isn't there some risk that the Church would be forced in some way to recognize or perform same-sex marriages?
No. Not so long as the First Amendment is in force.
Haven't churches in Canada been fined for preaching against homosexuality? Couldn't that happen here if same-sex marriage is legal in the U.S.?
Canada does not have an absolute constitutional guarantee of free speech as the U.S. does. The First Amendment completely protects freedom of speech and freedom of religious practice in the United States. No church (or individual) in the U.S. could ever be censured for teaching that homosexuality is wrong, or for refusing to marry or ordain a gay person without repealing the First Amendment first.
For example, the LDS Church did not allow blacks to be ordained to the priesthood or to be married in the temple until 1978. Despite the fact that Federal and State law prohibited discrimination on the basis of race, the Church was never required to change its policy and ordain blacks or marry blacks in the temple. The same would be true in relation to same-sex marriage.
Haven't religious agencies been forced to close down for refusing to give children up for adoption to gay couples?
Social service agencies, including religious agencies, that accept government funding, are generally required to abide by any antidiscrimination statutes in the jurisdiction where they provide services. For this reason, many religious social service agencies and educational institutions refuse state funding. So long as Church social service agencies do not accept state funding, they would never be required to provide services to gay or lesbian couples, including, for instance, placing children for adoption in homes led by gay couples, or offering marriage counseling to gay and lesbian couples.
Catholic Charities in Massachusetts was accepting state funding, and was told that they could not discriminate against gay couples seeking to adopt kids. Catholic Charities had the choice of refusing state funding, if they wished to continue their practice of declining to place kids with gay couples. Instead, they closed down operations in Massachusetts.
Haven't wedding professionals been fined for refusing to provide services for gay and lesbian weddings?
Individuals and Churches who provide public accommodations (such as renting church facilities to the general public) could be held liable for refusing to provide those accommodations to gay individuals on the same basis that they would provide them to anybody else. But discrimination in the area of public accommodations on the basis of sexual orientation is already against the law in Minnesota. Legalizing (or banning!) same-sex marriage would have no effect on this law as it already stands in our books.
A New Mexico photographer who refused to photograph a lesbian wedding was fined $6000 for violating the state's antidiscrimination law. The photographer was found guilty because she was found to be offering a "public accommodation," and the state antidiscrimination law forbids discrimination on the basis of sexual orientation in public accommodations. However, same-sex marriage is not legal or recognized in New Mexico. So it is misleading to imply that this antidiscrimination case was a result of legalizing same-sex marriage.