The USA star joined New York Red Bulls striker Thierry Henry at the top of the scoring charts on 11 goals with a second-half double as the Galaxy stayed on top of the Western Conference table.
Donovan opened the scoring with a brilliant goal in the 61st minute when he controlled with his chest before taking a first-time left-footed shot past Joe Cannon before following up with a penalty in the 75th minute.
He then turned provider ten minutes from time with a low cross from the left to the back post for Sean Franklin who slid home for his second in two matches before Adam Cristman grabbed the Galaxy's fourth with a 90th minute header after the Whitecaps failed to clear from a throw-in.
Elsewhere in MLS, Colorado Rapids defeated ten-man Philadelphia Union 2-1, Brian Ching netted a brace as Houston Dynamo beat Seattle Sounders 3-1 in Texas, Columbus Crew scored twice early to overcome Real Salt Lake 2-0 in Utah, Dwayne De Rosario scored both goals in DC United's 2-0 victory at San Jose Earthquakes, FC Dallas got the better of Chivas USA 1-0, Sporting Kansas City scored late to draw 1-1 with New England Revolution as Toronto FC came from two goals down to record a 2-2 draw at Portland Timbers.
2011 MLS season - Week 20 scores