So - your first step - to file your Canadian tax return as a nonresident
- and calculate possible tax liability
(if any) on that sale transaction.
Then - you will file your US tax return and will report that sale transaction on form 8949.
The gain is calculated as (selling price) MINUS (basis)
The basis is mainly your purchase price (assuming the property was purchased) adjusted by purchase and selling expenses.
As you held the property more than a year - the gain will be taxed at reduced rates - most likely - not more than 15%.
If the same income is taxable abroad and in the US - you may claim a credit for taxes paid abroad - so the same income would not be taxed twice. Use the form 1116
please find instructions here -
The credit is limited by the US tax liability on the same income - the form 1116 is used to calculate the amount of credit. Means - if tax liability abroad is higher - there will not be US taxes on that income, but if tax liability abroad is lower - in the US you will pay the difference after the credit will be applied.
Let me know if you need any help.