This list is a starting point, your specific situation may differ.
Business bank and credit card statements.
Many banks and credit companies provide this information online and can go back as far as seven years
Copies of cheques (often these are on your bank statements)
Listing of e-transfers sent and received
Documents that support your business transactions
Invoices that you have sent out to clients
Documentation for purchases you have made. Receipts, bills from vendors.
Loans that you have in the business name
Agreements that you have made that result in a financial obligation.
Lease, rental agreements etc.
Business Registration and incorporation documents.
Most recently filed Annual return (this is not your tax return) Incorporation documents Including:
List of shareholders and directors
business articles
Share structure and ownership
shareholder agreements.
Business registration and incorporation documents will be available from your lawyer. If you self-incorporated you likely do not have all of these documents.
Previously filed tax and information returns
If incorporated your last filed Corporate tax return (T2)
If self-employed your last filed personal tax return with the T2125
Statement of Business activities.
Copies of GST/HST/PST returns filed
Copies of T4 Summary and T4s filed if you have payroll
Copies of any T5018 (contractor payments) filed
Copies of any T5 Summary and T5s filed for shareholder (if incorporated)
Copies of any correspondence received from the Canada Revenue Agency
Copies of any correspondence received from your province (if you are
subject to PST).
Note that some of this information may be available online at CRA or your Province.
It may take a while to collect all of this information, but the best place to start is to connect with a professional who can provide more guidance on what information is required for your situation and what to do if some information is missing.