ING Direct is currently offering 2.5% interest for a 90-day GIC, 1% for 180 days, and 1.5% for 270 days.
What would be the advantage of locking my money in for longer if I'm just going to get paid less?
IMO this means one of two things:
the bank thinks that 3 months from now, the interest rates it plans to offer will be lower than 1%; after 180 days, it will go up again.
the bank needs more short-term cash than mid-term cash right now, so it offers you a better deal.
In either case, it is unlikely that your 90 day intrest rate will be available 90 days from now, and most likely it will be below 1% unless the bank yet again needs short-term cash from its customers.
With those proposed rates, I would go for half in 90 days and half in 270 days.
Disclaimer: am no economist, just spent a lot of time the past year fretting over the same kind of questions. Feel free to tell me where I'm wrong if you think I am.