You need to provide a bit more information: What are you marketing? A product? A service? Who are you marketing it to in the Cannabis market? Consumers? Growers? Processors? etc.
There are a couple of things you can do: check out the popular more consumer-oriented social media sites like FaceBook, Instagram, etc., and research their Cannabis communities, groups, etc., to see if they would be a good target for your marketing. Another approach would be to look at your competitors, potential advertisers, etc., and see where they advertise or platforms they participate in.
Smart way is to research your market, you need to know that perfectly, your competitors, their strategy, you should know your targeting audience and the most important channels of information. Probably you should concentrate your attention on social media
The best platforms for what? What type of cannabis do you want to market? You might not be able to market them on social media platforms unless you're authorized.
Nowadays, social media is the new trend of advertising. In doing so, check first your legalities to know your coverage.
The best tip for promotion is to follow the cannabis industry's social media pages and attend their monthly local meetings. and you can also put Google my business on your website, it will also give you some good results.
Find an influencer in the niche and pitch a joint venture opportunity to them about the product you want to sell.