Overnight or only for the shopping on Alberni? If the latter, I'd just do street parking. If overnight, some hotels have gated parking which may be a little more secure, but all underground. Further west of Granville would presumably be more secure than east of it. Nothing's totally safe but you can make your vehicle less of a target. If your car's really fancy, you might be able to have it parked in front of the lobby at Sheraton Wall Centre.