The man, from Quebec, was riding with another man from Vancouver to Montreal. He was hit at about 10:30 a.m. near the community of MacGregor, just west of Portage la Prairie.
When RCMP officers arrived at the scene, the man had been pronounced dead.
His name is not being released by police.
Police said alcohol is not considered a factor in the collision. There is no word on any charges.
Anyone with information about the incident is asked to call the Portage RCMP at 204-857-4445, or call Crime Stoppers anonymously at 1-800-222-8477. Anonymous tips can also be submitted online or by texting TIPMAN plus a message to CRIMES (274637).