I am looking to electrifying my tandem bicycle and one of my concerns is brakes. It currently has cantilever and I think that it will need to at least have V brakes if I convert it, if not disc brakes. While doing my research, I hear a lot about batteries and motors but can't find much information on whether ebikes are ok with V brakes or not, especially for a heavy bike.

So what do you guys say? Do all of you run disk brakes?

Personally I wouldnt consider riding one without disc brakes in the front @ least. It partly may be my riding style but my BB7's stop on a dime & they are amazing & have saved my hide more then once during last 13 months 5700 miles of riding. They make E-biking fun, part of what it's all about, quick lock ups keeping your balance without putting your feet down hit the throttle.
Your dealing with 30 more lbs. of weight knowing how fast disc brakes will stop you is a cool feeling.
Edit- forgot to mention the adjustments are just too easy, just reach down & one click of the dial inboard then outboard every once in a while when the lever gets low, my last front set of pads lasted over 3000 miles, simple to change, rears are original as mentioned 5700 miles.

I have regen breaking on my EPLUS which is OK 80% of the time , but for emergency I relay on my BB7 disc for stopping.
I would modyfy what was said above post,
I cannot imagine grinding mechanical breaks only for stopping with no regen breaking on any ebike.
Due to regen pads on BB7 will last and last.
On my TForce ebike front pads had not been changed for three /!!!!/ years.

How does the regen braking work? Does it activate a certain amount of braking as soon as you hit the levers? And then the pads start to work as you squeeze the levers more?

Or is there some way to modulate the regen?

on proper set up squeezing lever just a bit shoud activate regen, squeezing farther should start grinding pads.

I use grinding maybe on 10% of breaking. Reed sensor on break lever should be properly installed so only small amount of squeeze would activte regen.
Regen can be on/off types or modulated regen which fast gradually increase breaking force.

You can get away with a rim brake on the rear with high end pads (pad quality makes a huge difference on rim brakes) but for the front wheel at least I highly encourage both a disk brake and a strong fork to take the brake loads with the increased weight and speed and good brake on the front (your tandem bike probably already has a good strong front fork but mentioning it anyway).

The only e-bike I have that does not have at least a disk brake on the front is one that has a low speed geared down for torque hill helper motor that is only used while climbing hills at low speed and everywhere else its just a pedal only bike.

As to re-gen braking, yah, its nice but you only get that with a direct drive hub-motor or fixed chain drive set-up, internally geared hub-motor or mid-drive motor and you don't have any re-gen braking ability so insistence upon re-gen braking capabilities really narrows your motor type options.

There's no grinding for petes sake, if there's grinding your into the rotor.
No need for regen, hydraulics or even ABS on Motorcycles in my world for that matter,
Grinding, LOL

one of the futures of electric vehicle is regen breaking.
Of course you just use motor as generator which is great.
Fossil fuel vehicles cannot have it.

I can see regen on some cargo bikes & others my motto is to keep it simple & effective.
I worked for a Japanese car dealership in the early 1990's & we had a meeting with Nissan's higher ups who were making their rounds to newly opened dealerships, the reason why { back then ** the Asian cars were made better then most US cars was less parts & better engineering { theres like 1/3 less parts on Japanese cars back then **.
My bike has the brake cutoff switch when brakes/lever is applied . I'm not sure if regen would be suitable for my bike & riding.
I cant understand Hydraulic brakes on 60 lb ish 20 MPH bikes either, the feel of the mechanical brakes is part of what it's all about. brake fluid, lines to rupture. maybe on Stealths & optibikes it makes sense.

What weight and what speed?

I have canti on my tandem, which can be 500+lbs loaded for touring, and easily go 40mph in hilly terrain. Good brakes, good pads are better than cheap disk brakes. of course BB7 are the bomb.

Regen doesn't make sense on an e-bike. That is for an e-moped. Nothing wrong with that, but you are not going to want to pedal a regen bike.

You mean to pedal depowered ebike?
I pedal my throttle ebikes all the time along with motors and do not see any problems.
One of my ebikes EPLUS IS one of the most efficient ebikes you can find due to FOC + field weakening method of motor control and pedalling such ebike along with motor is a pleasure and excellent exercise.
I do not grind breaks a lot , I am on ELECTRIC vehicle. Especially when is wet.
It is all about how electronically ebreakes are implemented.

Weight is around 144 kg without cargo, if not less.

Can you give me details on how you setup the motor for low speed assist. I plan to do the same. Thanks