Manager Jeff Banister announced only the starters for the first two games Tuesday, when the team worked out at home before departing for Canada.
Gallardo (13-11, 3.42 ERA) won both of his starts this season against the Blue Jays, the only Texas wins against the AL East champs. The right-hander threw 13 2-3 scoreless innings, as Toronto had six hits and batted .136 against him.
The Rangers have won their past 10 games started by Hamels, including the regular-season finale Sunday with his complete game in a 9-2 win over the Los Angeles Angels to clinch the division title.
Hamels is 7-1 in 12 starts since Texas acquired him from Philadelphia in late July.