The 28-year-old Buchholz was designated for assignment on Tuesday. He was 1-0 with a 4.50 ERA in seven relief appearances with the Rockies.
Buchholz started the season in the minors while recovering from elbow ligament replacement surgery in 2009. He has a career record of 19-21 with one save and a 4.42 ERA over four seasons with Houston and Colorado.
The Blue Jays also moved righty Jesse Litsch to the 60-day disabled list on Thursday. He had season-ending hip surgery in early August and won't be ready until spring training.