The current Env. Can forecast for Ottawa has no temperatures below 0 C, with morning lows hitting zero Wednesday and Saturday.
On other hand, both the GFS and European model have morning low temperatures below zero Thursday through Saturday mornings, and maybe as soon as Wednesday.
How much faith do I have in Env. Can. temperature forecast? Cover the plants you don't want to freeze. Just sayin'.
PS. TWN has Saturday morning @ -2. That a bit better.