Harry Enten is skeptical:

We … know that single issues like marijuana usually don't move people who didn't vote before to go out and vote now. Ballot initiatives in presidential years only raise turnout by 0.7%. The age group of 18-29 year-olds, who are 2.5 times more likely to use cannabis, were not a larger percentage of the California electorate in 2010 compared to the previous midterm election, despite a legalize marijuana proposition being on the ballot. Voters also said that the proposition was not the reason they came out and voted.