I was doing a Google search, and I discovered an image on Google's homepage that honored the 31st anniversary of Canadarm's first use in space today, and Canadarm is to be featured on the new $5 bill to be released next year.
It seems as if the theme of the Frontier series ties in to an anniversary of a historical event in Canadian history, like the new $100 bill, released on the anniversary of the discovery of insulin, which was November 14 last year; and the new $20 note recently released last week, a Vimy Memorial theme just before Remembrance Day.
With that taken into consideration, and most new banknotes are normally first issued on a Wednesday (the only exceptions being the current $100 and $50 bills were first issued on a Monday), my prediction is that the new $5 note will likely be issued for the first time on November 13, 2013, the 32nd anniversary of Canadarm's first use in space. But, as with all predictions, take it with a grain of salt. The Bank of Canada may issue the new $5 note on a date that we least expect.
As for the new $10 note vs. the Trans-Canadian Railroad, I don't know exactly when the anniversary of its first use was, I thought I read somewhere the first runs (with Sir John A. MacDonald and somebody) were early in the month of July when it happened? I don't know the exact date of the Railroad's first use was, so I can place my money on the new $10 note being first issued anywhere between May and July 2013.