If you want to use other animation, you can use transitionBuilder, in your PageRoute. How you can use this represented for you below:
import 'package:flutter/material.dart';
main() {
  runApp(MaterialApp(
    home: Page1(),
  ));
}
class Page1 extends StatelessWidget {
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(
        child: RaisedButton(
          child: Text('Go!'),
          onPressed: () {
            Navigator.of(context).push(_createRoute());
          },
        ),
      ),
    );
  }
}
Route _createRoute() {
  return PageRouteBuilder(
    pageBuilder: (context, animation, secondaryAnimation) => Page2(),
    transitionsBuilder: (context, animation, secondaryAnimation, child) {
      return child;
    },
  );
}
And if you want to transition instantly, you can do this:
transitionDuration: Duration(seconds: 0)
This will decrease down the transition time to 0 second, which will eventually results to quick transition speed.
To know more about Page Animation Transition follow these articles:
- Page Route Animation
- Everything you need for Flutter Page Transition
You need to define something for your transition, if you don't want the default one, and this answer will help you achieve this.