Well, CIC will only count the 4 years before you apply for your citizenship, so at best you can only use days from the two years before getting PR.
Each day in Canada counts as half a day towards the citizenship count, but you can only claim a maximum of 365 days towards your "pre PR" total.
To get the full 365 days for those 2 years, you must have never left Canada during that time except for day trips (nothing overnight).
Be aware that all days spent outside Canada count against you when you are talking about citizenship.
I keep proof of all my travel outside of Canada, tickets, bookings, photos etc - It's just like gathering info for PR !
If I made it too confusing, tell me - it is late here