Alberta officially began granting marriage licenses to same-sex couples from July 20, 2005, pursuant to the Civil Marriage Act coming into force on that date. The Civil Marriage Act is legislation which legalizes same -sex marriages in Canada. This is a federal act, meaning that this law applies the same to all provinces throughout Canada.
Same-sex marriage was already legalized prior to 2005 based on case law, meaning the court granted decisions on same-sex marriage issues in certain provinces. Case law legalized same-sex marriages in numerous provinces, however, Alberta was not one of them. For example, the case of M v H  2 S.C.R. 3 was a Supreme Court decision regarding a same-sex couple and their divorce, rights, and equal treatment under the Canadian Constitution.
The parties and lawyers in the case requested the courts clarify the definition of spouse under the Divorce Act and declare this definition unconstitutional as it only related to opposite sex couples and excluded same-sex couples.
In the above case, M brought an application after the dissolution of her same-sex relationship with H. for Matrimonial Property division and Partner Support. She also challenged an Act that provided for marital support for opposite-sex couples but did not provide the same support for same-sex couples.
However, since the Civil Marriage Act came into force, same-sex marriage is legalized throughout Canada and its provinces. The Act states that Marriage “for civil purposes, is the lawful union of two persons to the exclusion of all others” instead of specifying a man and woman or opposite sex couples.
Since the Act coming into force, marriages are not void or voidable due to the fact that they are same sex marriages. However, the Act also states that religious officials are free to refuse to perform marriages if they are against their religious beliefs.
There are also numerous protections now for same-sex couples, for example, in the recent years and the Act coming into force, there have also been amendments to the Criminal Code of Canada regarding discrimination of same sex couples. Same-sex couples are also protected against discrimination under the Human Rights Act.
1Civil Marriage Act, S.C. 2005, c. 33
2M v H  2 S.C.R. 3
3Civil Marriage Act, S.C. 2005, c. 33