VIA OBS uses radio to communicate with each other, not the PA and intercom like Amtrak. That same channel is used by the SM to communicate with the engineer
CN has a nationwide "road channel"/train stand-by channel in Canada. RTC (dispatcher) communication is on a separate channel, much like CSX. The RTC Call In channels shifts by territory like US practice.
VIA OBS and head end communication:
160.200 (AAR channel 06)
CN nationwide train stand-by (road channel):
161.415 (CN channel 1, AAR channel 69)
Other CN channels used for RTC call-in that you may want to scan:
161.205 (CN 2, AAR 73)
160.935 (CN 3, AAR 55)
160.665 (CN 4, AAR 77)
Note that close to Toronto, the lines are now controlled and dispatched by GO Transit/Metrolinx, so they aren't on the CN channels any more. GO Transit is using NXDN digital transmission rather than analog. Unless your scanner had NXDN digital capability, you won't get anything except static bursts on your scanner on the GO frequencies, so I am not bothering to list them. The westbound Canadian will be on CN channels once it gets on the York Sub at Snider (you'll know because of the backup move to get on the York Sub from the Newmarket Sub). The Bala Sub shifts back to CN at Doncaster, the junction of the York Sub, so you are good from there on.
That is until the westbound gets on CP for directional running near Parry Sound for about 90 miles. CP's frequencies for that stretch are 161.325 road channel/train stand-by (CP 5, AAR 81) and 160.425 RTC Call In (CP 6, AAR 21).