Gay Parenting 101: Tools to Protect Gay and Lesbian Families - Part 1, Second Parent Adoption|
No, I'm not sure what the actual differences are (and I've just been trying to find out online without success).
About the only thing I know for sure is that income taxes are identical for legally married and common-law spouses here.
If I remember the situation correctly, back when the same-sex marriage challenges were happening, the government proposed to create a legal status which would be identical to marriage in every way, but not called "marriage" (a rose by any other name?). But the courts basically said "not good enough," and we got real same-sex marriage.