Given that all variables are the same, I presume that different
varieties of Rape(Canola) will produce different quantities of pollen
and nectar - please tell me if I am wrong! - you would even if I didn't
wish you to.
Are there any varieties in use that do not give nectar and or pollen?.
If so, what is likely to attract pollinators to the flower, as the plant
is a commercial concern there to produce seed in quantity and quality.
       I ask as last spring, year 2000, I noticed several areas of Rape
where bees were absent even though there were hives very close to the
said fields. The resulting honey crop was very low.

       Also, talking to various individuals in the agric. industry, it
seems to be an objective (for some crops) to make the bee redundant ,
and in some cases actually would be considered as a pest - e.g.. In the
production of seed or a particular cross for vegetable oil
The introduction of foreign pollen type may result in the production of
a seed containing the wrong " fatty acids", "genetic components","lower
yield" etc..

What says the group?

       Many of these comments come about during conversations where
pesticides are being criticized for their  limited discriminatory
activities.
       Hence, the argument goes, keep the pesticides and get rid of the
need for the bees(and at the same time, the annoying individuals
collectively termed Beekeepers- that is in polite circles.)

Peter