The top seed, who claimed the Montreal title in 2016, won seven of the last eight games as she wrapped up a straightforward victory over the 22-year-old Australian in one hour and 11 minutes.
"I think I played smart tennis today," said Halep, who broke Barty twice in the opening five games of the first set.
"I just went all the way also on her forehand, short, cross, long, everything. I played some slices.
"I think the match was a very good level of tennis even if the rhythm was a little bit mixed."
Halep, quoted on the WTA website, added: "I just want to give my best tomorrow and to enjoy the final because it's a great thing after a long break to play final at a big tournament."
In Saturday's second semi-final, defending champion Elina Svitolina, the number five seed, suffered a straight-sets defeat to reigning US Open champion Sloane Stephens.
The number three seed progressed to her third final of 2018, which will be a re-match of her French Open clash with Halep in June.
Svitolina's shaky start saw her give away her first two serves as she was taken to 4-0 by Sloane.
The Ukrainian eventually locked on in the ninth game to take a break of her own, but the burst was short-lived and she again lost her serve and with it the set.
With a 6-3 lead, Stephens kept her opponent working, breaking in the fourth game of the second set to pad out a 3-1 advantage.
Down but not out, Svitolina battled through a 13-minute game in which she took her opponent to three break points, but failed to convert.
She eventually managed to break the American in the seventh, but Stephens replied with her own and ultimately closed out the match 6-3 6-3.
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