how far in advance to buy VIA rail tickets Montreal-Quebec for cruise?

DH and I will be sailing on HAL Veendam from Quebec Sept. 12. We will fly into Montreal Sept. 6 and spend 4 nights there. I plan to take the VIA Rail train to Quebec, have the schedule printed and know which train I plan to take.

How far in advance should I purchase the tickets? Are there discounts for buying ahead of time?

like airlines they do have cheaper fares for booking early

http://www.viarail.ca/en/fares-and-packages

I should have booked when I first looked the schedule and fares up in March.

train 24 1:00pm-4:22pm was CAD$76 for 2 seniors on March 16

I just bought the tickets and they cost CAD$138 for 2. At least the exchange rate is better now. Should convert to $111 USD as of today on my credit card bill. Sigh. You learn.

My mom and I are sailing on the Caribbean Princess in October and we've booked already. My motto is "better safe than sorry"!! I am so looking forward to the whole trip, starting with the train ride :p

We just purchased our one-way, economy class, senior discount, tickets from Montreal to Quebec for the CAD$138 mentioned below. I couldn't see anything that would justify purchasing Business Class for such a short, mid-morning ride.