Registration for the offer is required and the offer is valid through April 30.
I wouldn’t make a transfer just to take advantage of this bonus, in general I find maintaining the flexibility of points to be hugely valuable. But if you’re considering or even potentially might transfer miles into Aeroplan, you should certainly register.
And Aeroplan is in general a great place to accumulate points (though you need activity in your account at least once a year to keep it active, and all points expire if unused after seven years). Their award chart pricing is good, they don’t block partner award availability as Star Alliance member United does, and their routing rules are great (eg US to South Asia via the Atlantic or Pacific or cross one ocean in each direction plus you get two stopovers rather than just one).