The order should be like this:
Solution 1:
1)首先找律师办单身证明,
2)去加拿大外交部盖章, get authenticated.
3)然后去大使馆办单身证明的公正, get authenticated
4)回国结婚
Solution 2: IF you are in China.
1)Get a so called 单身证明 (Single Status Statement) in Canada Embassy or any Consulor Offices by swearing there.
2)Register in a related chinese government office.
Note: Some registration offices in china accept Solution 1 but some others accept Solution 2. It depends on where you register in China. You have to check with the exact registration office before take any action.
FAQ
Why do I know this process?
I just helped one of my friends go through it.