I would assume it's similar if not the same as Russia.
Here's what we had to do:
- Get proof from Canadian Embassy that sponsor was never married before.
- Translate all documents into Russian - has to be validated by lawyer (in your case Ukrainian)
- Get officially married (In Russia it's ZAGS, not sure if it's the same in Ukraine)
- Get official translation of marriage certificate. (I recommend to make several copies)
Now I would recommend to take lots of pictures of the ceremony and if you going to have any celebration afterwards.
All in all the process took 3 months (post-soviet bureaucracy)