请教加拿大移民问题------语言能力证明

I received a notice from Canadian Consulate General.

They need a "Documentary evidence of your ability using the English language".

I am postdoc in the United States. I worked in the US for more than 3 years. I published more than 10 English papers.

Does anybody meet the same situation?
If yes, please tell me how to handle this.

Thank you very much.