The SSIA proceeds can be used after it finishes, or you could take (a large) tax hit, effectiuvely loosing your top-ups and use it now - I wouldn't reccomend this. You pension is tied up until retirement. A better option would be to go for a 100% mortgage for now and use the proceeds of the SSIA to pay down your mortgage when that it is finished. If paying both the mortgage and the SSIA is too much of a strain you could stop or reduce payments in to the SSIA for remaining term - in this way you still get the benefit of the top-ups you received so far.