Hi Kevin,
There is no perfect answer here. However, in my opinion one should only hold as many stocks as they can track and do their due diligence on. If you hold too many stocks, it can be daunting to stay on top of. Less concerning for blue chip companies like CP Rail, but very important for high-growth stocks like Shopify.
That being said, holding a large basket of stocks is typically done for diversification. Diversification helps reduce unsystematic risk - that is risk associated with a particular stock or industry. Systematic risk, is market risk - it is impossible to predict and impossible to diversify. Think COVID-19 and when the market crashed in March - no stock was immune.
I've done some research on this, and studies have shown that the benefits of diversification for the purpose of reducing unsystematic risk tops out around 26-27 stocks. Every stock added afterwards has limited, very small incremental benefit. Up until then however, the benefits to reducing unsystematic risk are meaningful.
Once again, 26-27 stocks may be too much. And you can still achieve decent diversification with 15-20 stocks - investors will just want to make sure that their holdings are spread out enough and that no one-company accounts for a significant percentage of their portfolio. I personally, have a 5% threshold - no company to account for more than 5% of holdings. I do allow for short term flexibility, especially if one of my stocks is performing well and jumps above 5%. As a I add new money, that position will usually come down. It is unlikely however, that I would add to it unless under special circumstances.
It's a personal choice, but hopefully my answer can help provide you with some guidance and context that will help with your decision making.
Mat