Federer has a 22-1 record on hardcourts this season after winning the Australian Open, Indian Wells and Miami Open titles earlier this year.
The Swiss star comfortably overcame 12th seed Roberto Bautista Agut 6-4 6-4 in the quarter-finals, but he feels he will have to be on top form to see off occasional practice partner Haase in Montreal.
“I’m looking forward to a tough match because he can serve very well and he mixes up his tactics a lot,” said Federer. “Sometimes he tends to just roll the ball in and use the big serve, or he uses a slice a lot and comes in.
“So I don’t quite know with Robin what I’m going to get. But, as I have practised with him quite a bit, maybe I am better prepared than if I would have never hit with him before.”
If Federer manages to overcome Haase he will face either fourth seed Alex Zverev or Canadian teenage wildcard Denis Shapovalov in the final.