My American girlfriend is visiting in the summer, we are flying in from working in Europe. Her plan is to stay for a week or two then head south for the rest of her trip (fly or drive).

I know she can legally enter for a 6 month period but does she need to show proof of onward movement?

Many thanks.

She can be admitted for up to 6 months, she can also be refused entry if the immigration officer sees fit. It it not a right of entry.

The biggest issue is going to be getting on a flight from Europe into Canada on a one way without residency. It would be far easier (and likely cheaper) to fly into the US then come to Canada.