I'm a USA citizen and my girlfriend is Canadian. We would like to live together in the windsor area and I want to travel back and forth to Detroit to work daily. Do I need to apply for a residence Visa or can I travel back and forth with my passport daily?
There is no such thing as a "residence visa". For US passport holders who are visa-exempt, each entry into Canada is assessed on the spot by CBSA. You need to prove to them you are a visitor to Canada, so not attempting to live here permanently. You will need to maintain a permanent address in the US.
Most US citizens can come and go from Canada as visitors, however if you attempt this every single day you should prepare that at some point, a CBSA officer may conclude you're trying to live permanently in Canada as a visitor, and deny you entry. The same would happen on the US side if it was your girlfriend attempting to do the same and live in the US as a visitor.
You will only qualify to apply for PR status in Canada, after you are common-law (so have lived together 12 months) or married to your partner.
It is much easier to live together 12 months and become common-law in Canada if you come as a visitor and simply stay here, so don't leave and enter frequently.