I paid capital gain tax with US brokerage in US tax return. If I report foreign tax paid for the gain in foreign income slip , will that be ok? not against treaty rule?

You would apply it under the FTC form, which can be located by clicking on the “Find” icon at the top right of your page and type in “Foreign Tax Credit” this will bring up the correct form to use to claim the taxes paid and ensure you are not doubled taxed.