The law is that recording of communication is lawful, so long as one of the intended participants in the communication. either the originator or the receiver, consents to the recording.
The consenting party does not have to let the other party know they are recording, HOWEVER:
Section 191(1) of the Criminal Code provides as follows:
Every one who possesses, sells or purchases any electro-magnetic, acoustic, mechanical or other device or any component thereof knowing that the design thereof renders it primarily useful for surreptitious interception of private communications is guilty of an indictable offence and liable to imprisonment for a term not exceeding two years.
So the recording must be made with a non-surreptitious device: an iphone, a go pro, a tape-recorder all qualify as non-surreptitious.
Source:
http://www.legaltree.ca/node/908