Strategy with mortgage

I'm close to signing a new mortgage, here the data:

- Quebec

- Best offer: TD @ 4.04% 3y + Instant access to margin on +0.2% which today makes it 4.65%

- Old house sold: 400k (mortgage free)

- New house: 650k

- Savings: 150k (TFSA)

Right now I'm doing it simple: 20% down-payment, 4.04%, 3y/25y and reinvest the 400k+ back on XEQT (restore tfsa and then non-reg). Seems somewhat OK, but taxes on non-reg may make it, at least early on, not great gains over the mortgage expenses.

But, I'm considering this alternative: 550k downpayment, so mortgage 100k, and access the instant margin to reclaim ~400k at 4.46% and then invest on XEQT. Which, it seems, would give me some tax break on the interest from the margin debt, right? Which means, I could reclaim back 2.23% yearly?

What am I missing here? Which is the best strategy?