Should I convert everything in Canadian dollars and calculate the canadian tax and minus the indian tax ?
Essentially this.
On your tax return you put the total amount, before deductions, of your Indian earnings converted at the Bank of Canada's average rate for the year (This goes on line 101). You then work out the Canadian taxes due on this income.
Then enter the Indian tax paid on schedule T2209 and then T2036 to calculate the federal and proincial tax credits. Again use the average exchange rate for the year. If the tax credits are more than the Canadian tax due then you owe nothing in Canada (but you don't get a refund). If the tax credits are less than the Canadian tax due then you have to pay the difference.
Be aware that foreign tax credits are a favourite object of audit by the CRA. Keep all documents that show the tax deducted. if you have to file a tax return in India the CRA will likley want to see this.