I have Capital losses from sale of shares that are not reducing my balance owed when entering my T5008s. Is there a maximum amount of Capital loss I can claim?

Capital losses are applied only against income from Capital Gains.  If you have no capital gains in 2017 your capital losses can be carried back against capital gains reported in 2014, 2015 or 2016 or they can be carried forward for up to 20 years.