Who can I appoint as Executor if I cannot think of anybody?

Your Executor appointment is an important one. You are trusting somebody to collect all of your assets and distribute them according to the instructions in your Will. This person must be strong with paperwork and numbers, as well as have the interpersonal skills to work with the beneficiaries when distributing the estate.
We would always recommend that you choose a friend or family member to be your first choice Executor. The Will gives them the power to hire professional help when needed, but it does mean that the administration of your estate will be handled on a more personal level. Your Executor can also be your main beneficiary, and this can often make sense if you are concerned about the estate being spent on Executor fees. 
Many people assume that one's spouse is the best choice for Executor, but this isn't necessarily a good idea. Firstly, assuming that your spouse is a similar age as you, by the time you die, and your Will comes into effect, your Spouse may also be 90 years old, and certainly not capable of working through the bureaucracy of things like filing your final year taxes. If you were to die suddenly, before you reach your senior years, your death may come as a shock to your spouse, and they may not be in a position emotionally to deal with paperwork and the dividing up of your estate. Furthermore, your spouse may just not be great with accounting.
If you have no family members or friends that have the profile needed, then you can turn to a professional lawyer. Be aware though that lawyers are expensive. They typically charge not only a significant percentage of the estate (usually set by Provincial law) but also an hourly rate. The task of administering an estate isn't really complicated, you just need to be methodical, and there are plenty of tools available to help. So it may be unnecessary to pay high professional fees for a straightforward estate, and remember, by appointing a friend or family member, they can hire a professional as and when they need help, without giving away a percentage of the estate.
Your next option, is any major bank. Most banks offer Executor services, but again, this can be expensive.
Finally, if you are completely stuck, every Province has an Office of the Public Trustee. If you really have nobody in your life who can be an effective Executor, and you don't want to deal with banks and lawyers, you can look up your Provincial Public Trustee and appoint them in your Will.