Do you report cost or market value of shares as part of foreign property declaration?

You would report the market value in Canadian dollars.

Thanks. If you have dividends paid out from these foreign shares, and they are already reported in T5 or T3 slips, do you still report them as income in the foreign property declaration form (T1135)

You don't have to report that you received the dividends. If you put the dividends in a foreign bank or reinvested them into foreign investments, then the dividend amount would be reflected there.