Recommendation
The most efficient mode of transport for your journey from Glasgow to Stirling-Rawdon, Ontario, is to travel by air. Given the considerable distance involved, flying is the quickest and most convenient option, allowing you to avoid lengthy travel times associated with land transport. You'll have the opportunity to experience a comfortable flight with reputable airlines such as KLM or Air Canada that offer competitive pricing and various flight times.
However, if you prefer a scenic experience and love train journeys, you can opt for a combination of train and bus, taking in the lovely countryside. Just be mindful it takes significantly longer.
In summary, for a balance between time and cost, I recommend flying from Glasgow to either Toronto Pearson International Airport or Ottawa Macdonald-Cartier International Airport, followed by a local bus or rental car to reach Stirling-Rawdon.