Obtaining tourist visa for HK-Beijing side trip by train?

I'm a Canadian passport holder looking at taking a side trip from Hong Kong to Beijing either by train or air. If I travel by air, I can pre-book and have my tickets for obtaining a tourist type before leaving Canada. However, If I book train tickets, I can't obtain the tickets until I'm in Hong Kong, so I can't submit them to obtain one before leaving. Is a L type required if entering by train? If so, how do I prove to the Chinese consulate that I will be entering/exiting on specific days?