He beat Argentine Juan Martin del Potro in the final in Montreal last year and is now targeting a fifth ATP Masters 1000 trophy and the 15th singles title of his career.
Murray is still searching for a new coach after he split from Maclagan, with whom he had worked for two-and-a-half years.
The pair teamed up in 2007, with Murray reaching two Grand Slam finals under his guidance before Maclagan was sacked after a meeting in Florida.
After playing in Canada, Murray will compete at the Cincinnati Masters in the build-up to the US Open, which begins on 30 August.
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