I have my L1A extended for a further 2 years pending the Adjustment of Status being applied for on our EB1C (I140 Approved, sat in Retrogression currently) - this will take us to Sep 2021 and five years into a potential seven if we only used the L1A/L2's.

Our two cars were leased on arrival through IAS on 3 year deals (October and December), so it is time to begin searching for their replacements. The question is not so much which car, but are we limited by the term of the I94 extension?

The original Lease cars were both for dates post the three years, but I do remember being told we wouldn't be offered 4 year leases for example. On a quick trek to look at some options the Toyota garage was not sure themselves if they could offer more than 2 years (which would be a problem if we wanted one through them as they were only offer 3+ year deals).

You should be able to lease for whatever period of time you want. In general, 36 months leases are going to be the best price but you might get a good deal on a 39 month lease if there is a regular autoshow in your area around 3 months from when you lease. Leases typically have a get out free clause if you can show that you are moving out of the county so that shouldn't be an issue if you get one for longer than you expect to be in the US and I don't think any dealership can ask for any immigration related information

Hopefully i can add some value here. Already financed 5 cars in less than 2 years and done a lot of research:

1. Please please note: Go for zero drive offs when you lease a car. That includes the 1st months lease. AIM for around 1% of the list price in monthly payments. i.e. $40,000 MSRP = $400 a month payment.
2. Various manufacturers will allow you to transfer your lease. I just did that with my X3 M40 on swapalease. Best ones are BMW, Ford, Toyota, Nissan.
3. Most leases are best over 3 years, but Toyota is one where 2 year deals can be better. It can be very model specific
4. Really try to get a good handle on what good lease prices are before you visit a dealership.
5. Leases will always have a buyout price, but as cars highest depreciation is in the first 2 years this will normally be higher than what the cars worth.

Some resources:

Edmunds car forums - this lets you check the residuals on leases and the money factor/interest rate a dealer should be charging you. Also any current incentives
Truecar - can help with what discount and rebates you may get
leasehackr - this is a great site. You can see what people are actually paying, offers from brokers showing prices by models and you can ask if you have a good deal.