Immigration Canada asked for a letter of explanation. Does this mean refusing a visa?

This visa has not been refused. Maybe the embassy wants to further confirm your information, so it requires you to write a letter of explanation, but it doesn't mean that your visa will be fine, because there will be an audit team at the later stage of the embassy. If the review team thinks that there are still some problems in some aspects of your information, it is still possible to refuse the visa.

Whether a general visa can be passed is related to the following factors: Have you ever been to a developed country like Canada? Are you married with children or single and divorced? What about the assets in your name? Do you have a steady job? Is the registered permanent residence in a sensitive area? Of course, if it is a post-audit, the embassy may check the authenticity of the information you submitted.

Normal is no problem, so you can get a visa smoothly under normal circumstances, don't worry too much.