PyQt5 figure canvas doesnt stretch

Problem is my FigureCanvas isnt taking all possible height, it is only reisizing its width. The problem occurs after resizing main window. I would like to let canvas take maximum available height.

This is how it looks now

This is minimal reproducible example:

import sys
import os
from PyQt5 import QtCore, QtWidgets, QtGui
from PyQt5.QtGui import (QPixmap, QPainter, QBrush, QPen, QColor)
from PyQt5.QtCore import *
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt5agg import NavigationToolbar2QT as NavigationToolbar
from PyQt5.QtWidgets import *
import matplotlib
from matplotlib import pyplot as plt

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("Distributions")
        self.setMinimumSize(480, 320)

        # Layout
        mainLayout = QVBoxLayout()
        dirLayout = QHBoxLayout()
        radioLayout = QHBoxLayout()
        canvasLayout = QVBoxLayout()

        # Setting main Widget
        self.mainWidget = QWidget()
        self.setCentralWidget(self.mainWidget)
        self.mainWidget.setLayout(mainLayout)
 

        # Setting canvas to plot
        mainLayout.addLayout(canvasLayout)
        figure = plt.figure()
        canvas = FigureCanvas(figure)

        toolbar = NavigationToolbar(canvas, self)
        canvasLayout.addWidget(toolbar)
        canvasLayout.addWidget(canvas)
        
        plotButton = QPushButton('Plot')
        canvasLayout.addWidget(plotButton, 
        alignment=QtCore.Qt.AlignCenter)
        plotButton.setMaximumSize(QSize(80, 60))
        
app = QApplication(sys.argv)
dialogi = MainWindow()
dialogi.show()
sys.exit(app.exec_())

>Solution :

You have to set the stretch factor when you add the widget to the layout:

canvasLayout.addWidget(canvas, stretch=1)