The new steak is described on the Taco Bell website as "tender-braised thick cut steak marinated in Chef Lorena Garcia’s authentic Latin recipe." The pieces also sport grill marks so I have to assume that the steak is grilled at some point.
Where chicken is featured for the Cantina Bowl (although steak and veggies are options), steak is promoted for the Cantina Burrito (although like the bowl, chicken and veggies are available options).
The new steak has already been available in several markets since last year, including my area, where I was able to check it out in the XXL Steak Nachos.
Here's the commercial Taco Bell put together to promote the new steak and the Cantina Steak Burrito:
Calories - 780 (from Fat - 250)
Fat - 28g (Saturated Fat - 7g)
Sodium - 1900mg
Carbs - 98g (Sugar - 7g)
Protein - 33g