In short, no. It is not instruction. A flight review is defined as a component of the recency requirements, which have clear guidelines that a flight review must be completed by a flight instructor. While that flight review could be conducted outside of an FTU, you have a Class 4 Flight Instructor Rating, which muddies the waters. Muddies them, but I do see a work around.
Here is the research and rationale.
We start with the need for a flight review in the first place, which only occurs if the other parts of recency are not met:
In CAR 401.05, when the paragraph is parsed together, we get a statement that reads that "No holder of a flight crew permit, licence or rating shall exercise the privileges of the permit, licence or rating unless that holder has, within 12 months preceding the flight, completed a flight review, in accordance with the personal licensing standards, conducted by the holder of a flight instructor rating for the same category of aircraft." Again, this only applies if the pilot has not met the other method of maintaining recency, which is simply flying once in the last five years.
Put into normal language: when required, a flight review must be completed by a flight instructor. So far, so good. You're a flight instructor, you can conduct a flight review.
But, you're a Class 4 Flight Instructor, meaning we have to look at the language surrounding supervision.
CAR Standard 421.62 states that "The holder of a Class 4 Flight Instructor Rating shall be under the supervision of f the holder of a Class 1 or 2 Flight Instructor Rating, in the applicable category..."
Yes, it follows on to say what documents shall be submitted for review to the supervising instructor, but that on its own cannot be used as an argument for using the flight instructor rating outside of supervision. Or, put in another way, just because you don't have to submit a flight review to your supervising instructor does not imply that you can use the privileges of the rating to conduct that flight review outside of supervision. You still have to be supervised to use your privileges, you just don't have to submit the paperwork to your supervisor.
Could you conduct a flight review outside of an FTU? Yes. There is no requirement that says the flight instructor must be attached to an FTU. They just have to have a valid rating. However, for a Class 4 flight instructor to conduct a flight review, you must still be supervised, which generally (although not a requirement) means you work for an FTU. If you could find a Class 1 or 2 who was willing to supervise you outside of an FTU, then as far as I can see, you're golden to complete the flight review.
Just make sure you have all your ducks in order, otherwise you're putting that other pilots recency in jeopardy as if you were not legal to complete the flight review in the first place, then they don't have a valid flight review, and any flight they take after could be in violation of the CARs, setting them up for a fine if TC ever found out.