[pcthrowaway]

Oh it's even worse, it mainly talks about advertising in "periodicals", but doesn't say anything about internet advertising (such as social media ads, paid sponsorships with influencers, sponsoring a github repo, etc.)

    You can deduct expenses for advertising, including advertising in Canadian newspapers and on Canadian television and radio stations. You can also claim any amount you paid as a finder's fee.

    Certain restrictions apply to the amount of the expense you can deduct for advertising in a periodical. You can deduct all the expense if your advertising is directed at a Canadian market and the original editorial content in the issue is 80% or more of the issue's total non-advertising content.

    You can deduct 50% of the expense if your advertising in a periodical is directed at a Canadian market and the original editorial content in the issue is less than 80% of the issue's total non-advertising content.

    You cannot deduct expenses for advertising directed mainly at a Canadian market when you advertise with a foreign broadcaster.

That section about the periodical having >=80% "editorial content" (whatever that means) is going to age well with LLM material sneaking in.