I've almost always excluded specific prior built or in-progress IP from my employment agreements without issue, as long as my employer's HR knows about it. Informing your employer of what you've created or are creating independently is almost always the best policy as it's unlikely they'll argue against it when it's early-stage (and you're protected if it becomes suddenly valuable).
More info http://www.cipo.ic.gc.ca/eic/site/cipointernet-internetopic....