The bad news first, CHEX (real CH-12) is facing what looks like insurmountable challenges due to distance, terrain, weak signal levels in the air and adjacent channel interference from the local (appropriately named) WHAM (real CH-13). If money and time are no object, a die hard DXer might try custom building a ganged array of Y10713's or similar DIY Yagi's. If so, there would still be no expectation of reliable reception, just the intermittent lucky 'skip' due to variable atmospheric conditions.
The situation for CBLT doesn't look much better, but one could go hunting for it if they had a capable UHF antenna such as the DB8E.
CIII (real CH-27) is possible according to the prediction shown. The DB8E mounted outdoors, clear of obstructions would be the smallest antenna I'd try.
Combining two antennas that operate in the same band (UHF in this case) is a challenge, The reversed splitter is the cheapest option, but least likely to to provide acceptable performance. The problem is that one antenna will receive what amounts to interference for the other antenna. Usually, the low levels of reflected/bounced signal will be ignored (to a degree) when only one directional antenna is used. But when the second antenna is added into the mix, much more signal from off angle directions are received, then mixed with the signals from the first antenna. This often results in less reliable reception of one or more signals that were received well by the original antenna.
I'd cable two separate antenna systems and terminate the second antenna in an axillary tuner:
http://forum.tvfool.com/showthread.php?t=2882