My experience with luggage in a roomette is the same as jp1822, although I wouldn't bring too much simply because of the cramped conditions. A fair-sized suitcase will fit in the overhead rack and there is space under the seat - in Manor sleepers, that is. Although I'm generally not fond of the Château roomettes, the "upper" ones (#3,4,7,8) have a large luggage space above - a solid alcove - which is very convenient. There is, however, no space under the seat in those roomettes.
The on-board baggage policy is unevenly enforced. In Toronto and Montreal (and a few others) station attendants patrol the boarding queue with a mobile scale. "Offenders" are sent to the ticket office to pay the fee for an overweight bag and if it's too heavy to be permitted on board they are required to empty some of it. There is even a scale in some of the Panorama Lounges. Many stations have been de-staffed recently. At some of these, passengers are expected to weigh their luggage at the ticket machines - as if most will do that! The same inconsistency applies to security: at some stations - Toronto and Montreal for sure - passengers' tickets, boarding passes or smartphones are scanned before they are allowed to pass through the gate. At most other staffed stations they are not. At unstaffed stations passengers sometimes board without a ticket because the kiosk isn't working or the passenger can't get it to accept their card. On Saturday at Toronto Union I met a small group of friends who are heading west on the Canadian. No-one weighed anyone's carry-on baggage in the Panorama Lounge or at the gate.