Canada officially recognized civil gay marriages in 2005 becoming the first country outside of Europe to do so. How it came about was individual provinces started legalizing it. The Supreme Court of Canada upheld in 2004 that civil marriages were the jurisdiction of the federal government. Since the federal government did not have a legal definition of marriage a bill was introduced and passed in 2005.
Keep in mind that in the United States, marriage laws are the jurisdiction of the states. Even the Supreme Court of the United States acknowledged in the Windsor case that marriage was a state-run institution. And states do have different marriage laws. Some states allow you to marry first cousins while others do not. Mississippi requires a blood test. Arizona does not.
In Canada back in 2003 the Supreme Court struck down several provincial laws against gay marriage stating that it was a matter of discrimination and in violation of the equality clause in the Canadian Charter of Rights and Freedoms from 1982. Keep in mind that the United States equality clause and the Canadian one are two different things. Also how the SCOC interprets law is very different than how SCOTUS does. SCOC tends to "legislate from the bench" and interpretations are more the the spirit rather than letter of the law.
Polls of Canadians at the time showed that Canadians were split about the issue of same-sex marriage. Split similarly to the polling of Americans today. Polls today vary but one 2012 poll indicated that 33% of Canadians do not approve of legalized same-sex marriage. Alberta, the most conservative province, showed that less than half approved of same-sex marriage.
Religious leaders have spoken out against legalized same-sex marriage in Canada including the Catholic Church. 43% of the population in Canada identifies as Catholic. Some provinces even go so far as to have a separate but public school system for Catholics. This has created much tension. The Bishop of Calgary, Bishop Henry, has received two human rights complaints through the Alberta Human Rights Act because he spoke out against homosexual acts.
Businesses have also received there fair share of flak. They either must stop providing wedding services altogether (alternatively shutting down their business) or face law suits and human rights complaints. The Knights of Columbus was sued by a lesbian couple. The couple won the suit even though as a religious affiliated organization the Knights of Columbus had the right to refuse the business from the beginning (but apparently not once the error was discovered). Individually owned businesses are not afforded that same right.
Education is also affected. Recently Premier Wynne, premier of Ontario (which is like a governor of a province) has rolled out a new sex education curriculum despite protests from parents. Keep in mind that this curriculum must be taught at all public schools including the Catholic public school systems. While the London Catholic School District has ensured that it thus far doesn't foresee problems integrating the sex curriculum into Catholic teaching, some parents remain skeptical. Alberta has come under fire from parents for forcing schools to form Gay-Straight Alliances if a student requests them. This measure didn't pass. Also Life Site news reports that two teachers have spoken about how they teach homosexual marriage and homosexuality to junior kindergarteners (who can start school as young as 3) and hidden in the math curriculum of grade 4-5 children against parental wishes. This is eerily similar to the David Parker case in Massachusetts, which so far allows the school district to teach about homosexuality and gay marriage without parental notification.
Polygamy also is getting it's fair shake in Canadian law. In 2005 and in 2007 questions were raised about the constitutionality of anti-bigamy laws in Canada. In 2011 The Supreme Court of British Colombia ruled to uphold current B.C. anti-bigamy laws. So far SCOC hasn't heard any cases on the subject, but it's important to note that no one has been prosecuted for bigamy in Canada since 2009. Ms. Barlow, whom the B.C. case was about, was denied permanent residency status. In contrast, the United States federal circuit court ruled that Utah cohabitation laws were unconstitutional (thus barring prosecution of adult polygamy), but that Utah could still bar issuing marriage licenses to polygamists.
There are lots of lessons to be learned from Canada about gay marriage. However I am hopeful that the US will do things differently. Marriage law is a state jurisdiction. We also have RFRA laws which hopefully will be also passed at every state level.