If you are self-employed, you can add internet costs to the business-use-of-home expenses (as an other expense) and it will be divided up based on how much of your house you use for work, like your other work-space-in-the-home expenses. A better option might be to add it to the regular business expenses (again as an other expense) so that you can pro-rate it based on business use.
If you are employed and your T2200 form from your employer says you can claim internet costs, then you can. But just like with a self-employed person, to may want to put it on the “Other Employment Expenses” page as an other expense, if you know how much you used it for work purposes.
For more information, please see your TurboTax article,
Which Home Office Expenses Are Deductible From Your Taxes?
Thank you for choosing TurboTax.