How to calculate stock income for new immigrants' first tax filing?

I purchased public stock share 5 years ago the cost was 100k, when I landed Canada 9th of Jul 2022 it's market price was 150k,  and I sold it out 120k 30th Dec 2022, should I declare it as gain 20 or loss -30? 
If it belong to loss, how can I prove its marketing price at 9th Jul 2022 was 150k?