Sanchez was an All-Star in 2016, when he went 15-2 with an American League-leading 3.00 ERA. But blisters on the middle finger of his pitching hand caused four stints on the disabled list last year.
The right-hander finished 1-3 with a 4.25 ERA and didn't pitch after July 19 last year.
"Sanchie, that was a big piece that was missing," Gibbons said. "He's coming off the year he won the ERA title. So it's vital that he pitches for us this year, I think, if we're going to do anything. Hopefully it doesn't flare up again on him."
Sanchez threw 34 pitches Saturday during his second bullpen session.
"He looks good. Second day he's thrown -- looks really good, feels good," manager John Gibbons said. "No signs at all of the blister, which is our No. 1 concern right now. For a guy who really basically missed a whole year -- actually, he looks pretty sharp to me."
"The injury bug got us in the rotation last year," Gibbons said. "I stack us up with anybody."
Toronto used a club-record 14 starters last season en route to a 76-86 record and fourth-place finish in the AL East. Only Stroman and Estrada made 30 starts.
"I think it's one of the best in baseball," Garcia said of the Blue Jays' rotation. "It's extremely talented. You've got anywhere from some of the younger best pitchers in the game to a couple guys that have been around like myself that compete."
Garcia threw his first bullpen session since arriving in camp Saturday.
Estrada worked during the offseason on his changeup and is pleased with the progress.
The right-hander felt like he had been slowing his arm speed at times when throwing the pitch.
"I threw a lot more changeups. I don't want to lose the feel of that pitch," Estrada said. "I struggled with it a little bit last year, and I kind of need that pitch. So I stayed on it and feels good right now coming out."