Can I be personally taxed on gains earned inside my own TFSA if it's reclassified as a business?

If CRA successfully recharacterizes active trading inside a TFSA as carrying on a business, the resulting tax is generally assessed against the TFSA trust itself, meaning the account loses its tax-free treatment for that income rather than the tax automatically being billed to you personally in every case. That said, whether or how personal exposure could follow beyond the account is genuinely fact- and case-specific, so it isn't accurate to say personal liability is either automatic or impossible.

This is a real and increasingly litigated area, not a remote or theoretical risk, and it shouldn't be understated just because the tax is technically assessed against the account rather than the individual directly. The practical effect for most people is still significant: gains you expected to keep completely tax-free inside your TFSA can end up taxed, which defeats much of the purpose of using the account in the first place. Because how this plays out depends heavily on the specific facts of the trading activity and how CRA and the courts have approached similar situations, anyone concerned about how their own trading pattern might be viewed should look at their specific circumstances rather than assuming a general rule either way.