In a guaranteed income endowment plan, the sum assured/monthly income that you stand to receive if you survive till the maturity of the policy term is guaranteed. In case of the death of the policy holder, the lump sum assured is guaranteed to the beneficiaries.
Bonuses may or may not be announced. If they are, then the total number of years that your policy has been in effect is factored in to arrive at your bonus amount. As such, the bonuses are not a guaranteed part of the policy.