I use around 400 MB a month, so like you, the 250 MB plan is too little and the 5 GB plan is too much.
If you aren't aware, Rogers has a $20 for 500 MB data plan for iPads. If you exceed the 500 MB, then you automatically get bumped up to the $35 for 5 GB rate. They call it the 'Flex Rate Data Plan for Tablets'.
http://www.rogers.com/web/content/i...y5jHECjCbVzp C VkzElCjCqBTwyl bVzp pzfz 5kzEl
This isn't a pay as you go plan, so you can't sign up for it over the iPad. You need to do it through a Roger's agent. The process is similar to signing up for a cell phone account and they give you a new SIM card.
I signed up for it a few weeks ago. It costs about $30 to set up the account (including the new SIM card). If I don't exceed 500MB, then I'll get that back in savings in a couple of months.
Just to add... I've heard that this plan allows for roaming in the US. I haven't confirmed it yet and don't know how expensive the roaming rate is.