Amplifying high frequency AC using op-amp or alternative methods
First of all: what you plan is dangerous. 100 Vpp can kill you if there's any beef behind the source, and your friendly national radio frequency regulation officials will kick in your door if you happen to emit a couple 100 W at 1 MHz as RF radiation. You've been warned.

100 V peak-to-peak load at 1 MHz isn't really trivial to deal with. Remember: any two conductors can form a capacitor. So, your high-voltage line in parallel to a ground plane will happily couple over energy. Make sure it doesn't – that might mean you'll have to construct things using enough spacing, or small enough dimensions, or with classical RF transmission line design. 

Now, when we're talking about voltage, we'll have to talk about impedance: 100 V into a 100 kΩ load is much easier than into a 50 Ω system. At these frequencies, you don't get around thinking about impedance matching – especially since things like reflections can lead to standing waves and dangerously high voltages >> 100 V in places you don't expect.

So, first of all, if all you need is an oscillator: Maybe build a high-power oscillator instead of amplifying a small one. That's quite possibly easier! There's a lot of oscillator circuits out there, and you can adjust a lot of them using some control voltage. You can build a simple control loop that compares the frequency (e.g. using a frequency counter from a microcontroller) to the should-be value and adjusts the control voltage accordingly.

Other than that: overpowered high-frequency resonant devices are the very classical domain of amateur radio designs. You can get power amplifiers for the 300 kHz - 3 MHz region relatively cheaply, even as military surplus equipment.

But: the easiest way is pretty simple: Build a transformer! You don't need amplification, i.e. an increase of power, you just want more voltage – if you can deal with a proportionate loss in current, then a simple 100:1 signal transformer will do your job; 1 MHz isn't hard for these, but 100 Vpp might be. Datasheet reading, it is.