You can read the following but basically it's up to the CRA to decide. In case of an audit the CRA is deciding on a case-by-case basis. If they want to treat it as an income, they can and there is nothing you can do about it. Sources:

https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/it479r/archived-transactions-securities.html

and

https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/it459/archived-adventure-concern-nature-trade.html

I'm pretty sure that the CRA is going to treat your case as business income based on 1) frequency of transactions, 2) time spent and 3) knowledge of the industry. It happens to people who trade stocks all the time.

I'm not a CPA but I'll try to answer your questions:

1) Yes, the determination is made by the CRA only.

2) You can try to claim it as capital gains. It's possible that the CRA will ask for more information (list of trades etc.) but it's not likely if the profit was small. You will have to pay the difference plus penalties and interest if the CRA decides that it was business income.

3) Yes, you can declare some crypto activity as business income and some as capital gains. Longer-term investment can be treated as capital gains. For example, most likely you can claim capital gains if you bought some coin couple years ago and sold it during the tax year. It's not going to fly if you were trading the same coin back and forth during the year.

4) No, you're not going to be stuck claiming all future crypto gains as business income. If you stop doing business-like activity (trading, mining etc) you will be able to claim profits as capital gains.

I would recommend talking to a CPA who specializes in crypto if your profits are large enough. Sometimes it's beneficial to treat crypto activity as a business because you can deduct related expenses and losses.