If the T5008 shows proceeds of disposition is less than the book value, can the difference be claimed as a a capital loss?

[Kyle_12]

Yes, when you sell or are considered to have sold, a capital property for less than what you paid for it you must report it as a capital loss. Capital losses are reported using schedule 3, may be used to offset gains within the current year, up to three years prior, or carried forward to future years, depending on the situation. 

For more information on Proceeds of Disposition and Claiming Capital Gains/Losses, see the links below:

Proceeds of Disposition 

Claiming Capital Gains and Losses