Is donor stewardship considered by CRA to be fundraising or a solicitation of support?

Yes. 

In the Fundraising Guidance CRA notes:

“Is donor stewardship a solicitation of support?

Donor stewardship occurs when a charity invests resources in relationships with past donors to prompt additional gifts. This could include providing donors with access to information, services, or privileges not available to others. These activities are considered solicitations of support.

Example
An arts charity invites only people who have given gifts above a certain amount to a private reception with the artists after a performance. The event is considered to be a solicitation of support.”

So there is nothing wrong with doing donor stewardship but the resources expended on it must be counted towards fundraising.

To review the CRA Fundraising Guidance see “How do I find the CRA Guidance on Fundraising for Canadian charities?” at
http://www.canadiancharitylaw.ca/index.php/blog/comments/how_do_i_find_the_cra_guidance_on_fundraising_for_canadian_charities/