I signed a document with someone else's name, forgery I guess. If I am found guilty, what type of sentence will I get?

Did you sign someone's tax returns, credit card application or... Statement to the FBI or someone's birthday card?

What country and state or province would this be... laws and punishments vary widely depending on where you are.

I am in New Brunswick , Canada. I signed a document with the persons consent and approval as a matter of convenience and now they are saying they didn't. Court case is a little iffy as I have some material that implys they were aware of this. The problem is, we were business partners and I have since terminated the business relationship with my partner and continued on solely. This did not sit well with my bus partner and now they are denying giving permission. It is basically payback for eliminating them from the business arrangement.

... forgery I guess. ...

Don't guess. Your attorney should be able to tell you exactly how the crime with which you are charged is defined. Either what you did is a crime or is not a crime. No guesswork belongs here.

For example, the crime may be to sign someone else's signature with the intent to defraud. If you didn't have that intent you are not guilty.