Couple of things first, Alfa_uno...
Here are the criteria from the Web site:
An income replacement program that ensures your income does not fall below 75% of your gross pre-release military salary. This benefit is taxable and is payable while you are taking part in the rehabilitation or vocational assistance program. The Earnings Loss Benefit will ensure that you have a total pre-tax income of at least $40,000 per year (with the exception of some reservists).
You may qualify for the Earnings Loss Benefit if you are:
•a CF Veteran who is eligible for the Rehabilitation Program or vocational assistance services from VAC; or
•the survivor of a CF member or Veteran who died due to:
◦a service-related injury or disease; or
◦a non-service-related injury or disease aggravated by service.
I'm not sure what the top-up is based on, not in my arcs, but I can find out for you. As for the docs, you can get a copy of your MPRR either from your OR or EMMA (if still serving), or it may already be on file with VAC, if you are a client. Otherwise, they should be able to request it from your last unit or Ottawa, ditto the rest of the docs you're looking for.
Best bet is to call the 1-800 line, or visit your VAC District Office (I prefer face to face myself).