I have a customer who wants to hunt Canada but has a OWI about 5 years ago. Any issues crossing the border. Can't seem to get the same answer from Canadian authorities.

Yes, they will have issue unless all the proper paperwork is completed.

There are forms to fill out and a fee (go figure) and it can take some time to complete the process.

check out this link:

http://www.cic.gc.ca/english/i.../5312ETOC.asp#5312E3

It is up to the agent's discretion at the border. They can issue a temporary visa or they can deny entry. The best thing to do is get approval of rehabilitation and then your client will have no issues.