are you looking for a forecast or for a current obs type thing.
for the above graph you may find it easier to read the actual data instead of trying to interpet the graph.
notice by clicking on any station you get data where you can look at both dew point and temp to see where they are the same..like above when lines are close together or you can look to the column on the right for the relative humidity value..70 and above is good for clouds and the column on the far left will give you the height in metres
Sounding
you could also utilize environment canada's cloud forecast model based on the GEM regional model, this is like looking at a sattelite picture but it is forcasted..you use the same idea as looking at a sattelite except it is a forecast..this is good out to 48 hours and you choose between eastern us and canada and western us and canada
below the models is an explanation on how to judge cloud height...between low, mid and high..not specific elevations
Cloud Forecast
hope that helps, spend some time figure it out may make or break that next trip
cheers