On a soaking day at the grasscourt championships, Hewitt managed to survive numerous rain breaks to book his place in the fourth round for the sixth time in his career.
Canas missed last year's tournament while serving a doping suspension and reached the last eight at the French Open four weeks ago.
Australian Hewitt, who is the only former champion alongside Roger Federer in the men's draw, will next face either fourth seed Novak Djokovic or Germany's Nicolas Kiefer.
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