The current food on "the Canadian" is nowhere near the golden age of RR dining cars. It's a step up from Amtrak for sure but when stocking the diner in Winnipeg it was all boxes from Sysco.
I can't speak for Rocky Mountaineer but I didn't think they even had dining cars.
IMO, and in all Honesty, as One who actually is Old enough to have ridden on ,and got to eat in the Diners on such Trains as The Super Chief, The Sunset Ltd., The Texas Eagle, The Southern Crescent, The Panama Ltd. etc. I agree!
But the Canadian IS the Closest one can come to "Old Time" Diner Food and Service without Paying a Fortune to Ride on for Profit Private Rail Excursions! I thought the Canadian Food and Service was Better Than the SP Diner on the Sunset Ltd., but not the Santa Fe Super Chief which was the Best Travel Food and Service I ever had!!
YMMV