Originally Posted by Chef Dave
In general, one solid fat may replace another ... and one liquid fat may replace another ... but liquid fats should not be used as substitutes for solid fats.
Part of the reason has to do with fat content. Shortening has a higher fat content than canola oil. Fats with less than 80% fat content will affect the taste of your product.
We're not talking about "...In general...." We're talking specifics, in this case, banana bread. The fat content of canola oil is more than sufficient to coat the flour and not interfere with the liquid content.
Not speaking in theory, but in practical experience, I have interchanged them with success.