Canizares birdied his closing two holes to finish with a 68 at Wentworth for an overall 9-under 207.
Westwood made eagle on the par-5 fourth and finished it 208.
If Westwood wins, he would set the record for the most appearances before winning the event for the first time.
Canizares' best finish at Wentworth was 10th four years ago.
"I know that people will look at the leaderboard and would assume Lee (Westwood) is going to win. But this sport has proven that it's not always what it looks like," the 30-year-old Spaniard said. "Anybody within five shots of the lead has an opportunity to win, so you never know."
Westwood lost in a playoff here to Luke Donald two years ago.
"I've now been coming here 20 years and it would feel great to win," Westwood said. "But then I've always played well around here and I feel the course suits my game."
Scotland's Marc Warren (70) and Italy's Matteo Manassero (69) are tied in third place on 7-under.
Spain's Sergio Garcia, whose verbal sparring with Tiger Woods turned ugly this week when he said he would "serve fried chicken" if he had dinner with the American, posted a 68 for an eight-way share of sixth place—only four off the lead.
"There's no doubt that everybody has made this week easier for me," said Garcia, who has publicly apologized for the remark. "They have been amazing, at every single tee, every single green