There are basically 3 route options for driving between Whistler and the US. One is to follow Hwy 99 right through Vancouver and across the Peace Arch Crossing at Blaine, WA to Interstate 5 in Washington State.

The second is to follow Hwy 1 east to 176th St in Surrey which is Hwy 15 (Pacific Highway) and across the Pacific Crossing at Douglas, BC to US Hwy 543 (Truck Route) and on to Interstate 5.

The third is to follow Hwy 1 farther east to 264th St and turn south on Hwy 13 (Aldergrove-Bellingham Hwy) to the Aldergrove Crossing where the US highway 539 is called Guide Meridian Road.

The latter two look farther, but traffic tends to move along most of the day. Peace Arch can be backed up with traffic for several hours.  On weekends and in the summer when people are travelling, the easterly two crossings have an advantage.

Between Bellingham and Whistler, the Peace Arch route comes in at 2.5 hours, 207 km. The Pac Hwy one comes in at 2.5 hours, 205 km. The Aldergrove route comes in at ~3 hours, 213 km, all according to Google maps. Plus any border wait or traffic congestion anywhere. If Peace Arch has a 3 hour wait at the border the other two routes have an advantage. They don't get the same waits.

Radio stations AM 730 and AM News1130 broadcast traffic, border and bridges, congestion and weather.

The following border web cams, during daylight hours here, show what live traffic conditions are like at the three crossings.

http://www.borderlineups.com/cam.php?...

http://www.th.gov.bc.ca/ATIS/

 A good border app showing wait times is "Border Check".